There is no clocking of the barrel nut on the M4E1 or M5E1 and the handgaurd just slides on and is attached with screws to the boss that is part of the forging. It really doesn't get much simpler. It makes for basically a monolithic upper/rail.I was very close to trying the AP rail with the M5 upper I'm using on my current X-Caliber 16" build, the combo looks good. I decided to stick with the OdinWorks 12.5 keymod I used on the 18". I don't know much about the AP rail installation, OdinWorks installation is a breeze, and I like not having to "clock" barrel nut. It might be the same with AP, just don't know.